This study employed in vitro seed culture to determine how C and N supply influence the growth (i.e. starch accumulation) and protein composition of maize (Zea mays L.) endosperm. Immature kernels were grown to maturity on liquid medium containing various concentrations of C (sucrose at 234 millimolar [low] and 468 millimolar [high]) and N (amino acid mixture ranging in N from 0 to 144 millimolar). Low C supply limited starch, but not N, accumulation in the endosperm. With high C, endosperm starch and protein content increased concomitantly as N supply increased from 0 to 13.4 millimolar. Endosperm growth was unaffected by additional N until concentrations exceeding approximately 72 millimolar reduced starch accumulation. A similar inhibition of starch deposition occurred with lower N concentrations when kernels were grown with low C. Endosperm total N content reached a point of saturation with approximately 36 millimolar N in the medium, regardless of C supply. Zein synthesis in the endosperm responded positively across all N levels, while glutelin content remained static and albumin/globulin proteins were reduced in amount when N supply was greater than 36 millimolar. A reciprocal, inverse relationship was observed in mature endosperm tissue between the concentrations of free amino acids and soluble sugars. Our data suggest that under N stress starch and protein accumulation in the endosperm are interdependent, at least in appearance, but are independent otherwise. 相似文献
Field grown maize (Zea mays L. cv B73 × Mo17) plants, with and without ears, were sprayed with urea solutions to determine whether foliar application of N could prevent or delay the accelerated loss of reduced N from the leaf and leaf senescence induced by ear removal. Urea sprays were applied at 7, 14, and 21 days after anthesis in three separate and equal applications that provided a total of 67 kilograms N per hectare or 1 gram N per plant. Treatments were arranged in a 2 × 2 factorial in a randomized complete block with five replicates. Appropriate plant and leaf samplings and assays were made.
In response to spray treatments, net increases of reduced N were detected in the whole shoot and plant parts, especially the stalk of the earless plants and grain of the eared plants. There was no effect of urea spray treatment on the normal loss of N from the leaves or rate of senescence of the eared plants or on the accelerated loss of N from the leaves or rate of senescence induced by ear removal. Grain and stover yields were unaffected by the spray treatment.
Apparently the plants were unable to utilize the urea N applied to the vegetation (primarily leaves) after anthesis to enhance or extend the accumulation of dry weight by either eared or earless plants.
To examine the effects of N nutrition upon endosperm development, maize (Zea mays) kernels were grown in vitro with either 0, 3.6, 7.1, 14.3, or 35.7 millimolar N. Kernels were harvested at 20 days after pollination for determination of enzyme activities and again at maturity for quantification of storage products and electrophoretic separation of zeins. Endosperm dry weight, starch, zein-N, and nonzein-N all increased in mature kernels as N supply increased from zero to 14.3 millimolar. The activities of sucrose synthase, aldolase, phosphoglucomutase, glutamate-pyruvate transaminase, glutamate-oxaloacetate transaminase, and acetolactate synthase increased from 1- to 2.5-fold with increasing N supply. Adenosine diphosphate-glucose pyrophosphorylase and both ATP- and PPi-dependent phosphofructokinases increased to lesser extents, while no significant response was detected for hexose kinases and glutamine synthetase. Nitrogen-induced changes in enzyme activities were often highly correlated with changes in final starch and/or zein-N contents. Separation of zeins indicated that these peptides were proportionately enhanced by N supply, with the exception of C-zein, which was relatively insensitive to N. These data indicate that at least a portion of the yield increase in maize produced by N fertilization is induced by a modification of kernel metabolism in response to N supply. 相似文献
Visual senescence symptoms and associated changes in constituent contents of three field-grown maize (Zea mays L.) hybrids (Pioneer brand 3382, B73 × Mo17, and Farm Service brand 854) were compared in response to ear removal. Whole plants were harvested at eight intervals during the grain-filling period, and analyzed for dry matter, total N and nitrate N, phosphorus, sugars, and starch.
Upper leaves of earless P3382 and B73 × Mo17 showed reddish discoloration by 25 days after anthesis (DAA) and all leaves had lost most of their chlorophyll by 40 DAA. In striking contrast, leaves of earless FS854 plants remained green and similar in appearance to eared controls throughout the grain-filling period.
For all hybrids, ear removal led to a decrease in dry weight, reduced N, total N, and phosphorus contents of the total plant, and an increase in carbohydrate content of the leaves and stalks, relative to respective controls. Although changes in carbohydrate and N contents, which previously had been associated with senescence, were observed for all earless hybrids, these changes were followed by accelerated senescence and early death only for P3382 and B73 × Mo17. By 30 DAA, earless P3382 and B73 × Mo17 plants ceased to accumulate dry weight, total N, and phosphorus, indicating a termination of major metabolic activities. In contrast, earless FS854 plants retained a portion of these metabolic activities until 58 DAA, indicating a role for roots in determining rate of senescence development. Thus, the course of senescence was more accurately reflected by measurements of metabolic activities than by measurements of metabolite contents at any given time. These results show that the ear per se does not dictate the rate or completion of the senescence process, and implicated an association between the continued accumulation of N and associated root activities with the delayed senescence pattern of the earless FS854 plants. It is evident that studies involving control of senescence among species must also consider genotypic influences within species.
Changes in dry weights, reduced N, nitrate, and nitrate reductase activity of various plant parts of the above ground vegetation (stover) and ears of field grown maize were measured at intervals between anthesis and grain maturity. Nonstructural carbohydrate contents were also measured in some instances. Changes in dry weight and reduced N content were used to approximate net in situ photosynthetic and nitrate assimilation activities and to determine whether the availability of photosynthate or reduced N was limiting grain production. 相似文献
Four maize hybrids, two with high and two with low levels of postanthesis nitrate reductase activity were grown under field conditions. The characteristic enzyme patterns had been established in previous work. Nitrate reductase and proteases were measured in three representative leaves (ear leaf, fourth leaf above and fourth leaf below the ear) at intervals throughout the period of grain development. Concurrent with enzyme sampling, other plants were harvested and subdivided into top, middle and lower leaves, husks, stalks, and ear. Dry weights, nitrate, and reduced N were determined on all plant parts for each sampling. These data established the rate of N accumulation by the grain and depletion from the vegetative material and provide some insight into the relation between newly reduced and remobilized N and accumulation of grain N. Other plants were harvested at maturity for yield and harvest indices for dry weight and N. 相似文献
Ears were removed from field grown maize (Zea mays L.) to determine the effects on senescence and metabolism and to clarify conflicting literature reports pertaining to these effects. Ears were removed at three days after anthesis and comparisons were made of changes in metabolism between eared and earless plants until grain of the eared plants matured as judged by black layer formation. 相似文献
Tropical maize is an alternative energy crop being considered as a feedstock for bioethanol production in the North Central and Midwest United States. Tropical maize is advantageous because it produces large amounts of soluble sugars in its stalks, creates a large amount of biomass, and requires lower inputs (e.g. nitrogen) than grain corn. Soluble sugars, including sucrose, glucose and fructose were extracted by pressing the stalks at dough stage (R4). The initial extracted syrup fermented faster than the control culture grown on a yeast extract/phosphate/sucrose medium. The syrup was subsequently concentrated 1.25–2.25 times, supplemented with urea, and fermented using Saccharomyces cerevisiae for up to 96 h. The final ethanol concentrations obtained were 8.1 % (v/v) to 15.6 % (v/v), equivalent to 90.3–92.2 % of the theoretical yields. However, fermentation productivity decreased with sugar concentration, suggesting that the yeast might be osmotically stressed at the increased sugar concentrations. These results provide in-depth information for utilizing tropical maize syrup for bioethanol production that will help in tropical maize breeding and development for use as another feedstock for the biofuel industry. 相似文献
The demand for biofuels has created a market for feedstocks to meet future energy requirements. Temperate × tropical maize (Zea mays L.) hybrids, which combine high biomass and fermentable stalk sugars, have yet to be considered as a biomass feedstock. Our objective was to evaluate biological potential, genetic variability and impact of nitrogen (N) on biomass, stalk sugar, and biofuel potential of temperate × tropical maize (TTM) hybrids. Twelve TTM hybrids, two grain and silage hybrids were grown in 2008, followed in 2009 by seven earshoot‐bagged TTM hybrids. In both years, they were grown with and without supplemental N (202 kg ha?1) in Champaign, IL. Plants were sampled for total and partitioned biomass, and analyzed for concentration and content of sugar. The TTM hybrids were 40% taller, exhibited later reproductive maturity, greater flowering asynchrony, and remained green longer. All hybrids responded to supplemental N by producing more biomass and grain, a lower percent of biomass partitioned to stalk and leaf, whereas TTM also had a decreased concentration of sugar. Total average biomass yields were 24 Mg ha?1 for both the TTM and grain hybrids. However, TTM partitioned 50% more biomass to the stalk and produced 50% more sugar, and had less than half the grain of the commercial hybrids, indicating grain production and sugar accumulation are inversely related. When grain formation was prevented by earshoot bagging, TTM hybrids produced, without supplemental N fertilizer, an average of 4024 kg ha?1 of sugar, which was three‐ to four‐fold greater than the non earshoot‐bagged TTM and ear removed hybrid. Calculated estimates for ethanol production, considering the potential from sugar, stover and grain, indicate TTM can yield nearly the amount of ethanol per hectare as modern grain hybrids, but with a decreased requirement for supplemental fertilizer N. 相似文献